In the railroad industry, whenever it is necessary for one rail to cross over another, as in a turnout or crossing, a railroad frog is used to facilitate the crossing of the train's wheel over the intersecting rail. Originally, railroad frogs were constructed of rail sections, flangeway filler bars, and blocks bolted together. This style of railroad frog was not very desirable because the train wheel, riding on its tread, would have to “jump” across the flangeway of the intersecting rail, resulting in severe impact on both the train wheel and the railroad frog. This severe impact caused damage to the railroad frog, the train wheel, and the roadbed, not to mention passenger discomfort and undesirable noise.
As railroad tonnage and use increased, railroad frogs were developed that allowed train wheels to pass over the flangeway gap by riding on their flanges rather than their treads. This is accomplished by diminishing the depth of the flangeway in the area of the gap so that the flange contacts the flangeway floor, lifting the tread slightly above the top of the rail and supporting the wheels full load. Upon passing over the intersecting rail's flangeway gap the flangeway depth increases, resulting in the tread once again contacting the top of the rail and the flange being lifted from the flangeway floor. Existing flange bearing railroad frogs accomplish this lifting and setting-back down of the tread by linearly ramping the flangeway floor. Flange bearing railroad frogs are typically constructed of cast manganese for increased strength and durability. While at one time flange bearing railroad frogs were used solely for light weight transit systems, their application has become standard in the industry. Examples of flange bearing railroad frogs are described in U.S. Pat. No. 5,845,881, Young et al., and U.S. Pat. No. 5,746,400, Remington et al., the teachings of which are hereby incorporated by reference in their entireties.
For a single railroad intersection (i.e., where one set of railroad tracks crosses another), a total of four railroad frogs are used. A frog must be connected to each of the intersecting running rails (i.e., the rails on which the train actually travels) on both sides. Thus, each frog has four running rail connection areas positioned so that the flange of the train wheel can properly enter and exit the flangeway of the frog and remain travelling on the running rail. Traditionally, the connection areas of railroad frogs are made from manganese steel castings that are bolted to the running rails.
Referring to FIG. 1, prior art railroad frog 100 is illustrated. Prior art railroad frog 100 is of the bolt connection type and connects to running rails 105 and 110 via bolts (not shown) that extend through bolt holes 120 and corresponding holes of rails 105 and 110. Nuts (not shown) are then used to threadily engage the bolts, thereby securing the running rails 105 and 110 to prior art railroad frog 100. Connecting railroad frogs to running rails via bolted connections has proved to be less than optimal. As time passes, bolted connections are subjected to repetitive loading and unloading by trains crossing the frog time and time again. These loading-unloading cycles, and the vibrations associated therewith, eventually cause the bolted connections to loosen. Loosening of the bolted connections is exacerbated due to rail batter.
Loosening of bolted connections requires consistent maintenance that can be cumbersome, time consuming, and expensive. The problems and costs associated with maintaining bolted connections are significantly increased for tracks that are buried under pavement or dirt because the pavement needs to be dug up to tighten the bolts. Moreover, the “play” in loosened bolt connections can cause potholes in the pavement near the connection.
Thus, a need exists for a railroad frog suited for better connection to the running rails. While attempts have been made to more effectively connect running rails to manganese steel cast frogs, these methods are either ineffective or expensive. Attempts have been made to eliminate the need for bolted connections by welding the running rails to the manganese cast frog connection points. However, because running rails are typically made of hardened steel, not manganese, it is very difficult, if not impossible, to achieve an acceptable weld between manganese and hardened steel due to the differences in material properties (such as heat conductivity, weight, etc.). In attempts to remedy these welding problems, methods have been developed where one or more intermediate pieces, such as a bainic steel piece and/or a pearlitic steel piece, are first welded to the frog. Such methods are disclosed in U.S. Pat. No. 5,170,932, Blumauer, and European Patent Applications 0602728 and 0602729, both Connelly, et al. However, these methods require that multiple welds be made for each connection. The existence of multiple welds per connection results in an increased probability that a weld will eventually fail. Additionally, these welds are very difficult to achieve and either require special equipment or can not be easily performed in the field.
While steel cast railroad frogs do exist that are capable of having running rails welded directly thereto, these welds are often difficult to properly perform and/or result in less than optimal welds. This is due to the configuration of the connection areas of the frog to which the steel rails must be welded.
An additional problem with existing railroad frogs is that of rail batter. As a train crosses a frog and transitions from being supported by the running rail to being supported by the frog, which also corresponds to the transition from tread support to flange support, the flange of the train wheel impacts the linearly ramped floor of the flangeway, resulting in impact on the wheel and the frog. This impact not only damages the frog and the wheel, but also causes unwanted vibration throughout the system that can loosen or otherwise compromise joint connections. This is known as rail batter. It is believed that the problem of rail batter can be reduced by properly modifying the surface geometries of the flangeway floors of the frog.
Referring now to FIG. 2, a cross sectional view of flangeway 130 of prior art railroad frog 100 (FIG. 1) is illustrated. The cross sectional view of FIG. 2 is take along lines 2—2 of FIG. 1. Flangeway 130 has a linearly ramped floor. When a train wheel (not illustrated) is travelling through linearly ramped flangeway 130 from left to right, the initial flangeway depth is deep enough so that the flange portion of the train wheel is not in contact with horizontal floor 131. As such, the tread of train wheel rests on top surface 140 of the flangeway wall. As used herein, flangeway depth is equal to the vertical distance from the floor of the flangeway to the top surface of the flangeway wall. As the train wheel proceeds through flangeway 130, the train wheel will contact linear ramp 132. As the train wheel continues up linear ramp 132, the flangeway depth linearly decrease until, at some point, the tread of the train wheel is lifted from top surface 140 and the load of the train is supported solely by the flange. The train wheel flange continues along floor 133 until it starts travelling down linear ramp 134. The flangeway depth decreases as the flange travels down ramp 134 until a point is reached where the flangeway depth is greater than the length of the flange. At this point, the tread of the wheel contacts top surface 140 and supports the load once again. Because ramp 132 and 134 are linear, the train wheel flange abruptly contacts ramp 132 upon entering flangeway 130, and the train wheel tread abruptly contacts top surface 140 upon leaving fangeway 130. These abrupt contact points put great stresses on the train wheel, the prior art frog 100, and the bolted connections. As a result of these stresses, damage and vibration occur.